As you may know, Amazon Prime subscribers can freely borrow a book a month from the newly created Kindle Owners’ Lending Library. Its catalogue currently boasts 75,000 titles thanks to Amazon’s Kindle Direct Publishers Select program.

Also known as KDP Select, the initiative rewards self-published Kindle authors and publishers who make their books exclusive to the Kindle Store for at least 90 days by entering them into the Kindle Owners’ Lending Library.

As we recently reported, Amazon has announced a $6m annual fund to support the program, with $500,000 set aside for the month of December. According to the company, KDP authors who participated in the initiative have already earned $1.70 per borrow.

As a result of what it describes as a very strong start for its Lending Library, fueled by record holiday sales, Amazon has also added a $200,000 bonus to the January KDP Select fund, raising the total monthly pool from $500,000 to $700,000.

While free lending certainly fostered the interest in these books, Amazon points out that sales increased as well. Says Russ Grandinetti, VP of Kindle Content:

“KDP Select appears to be earning authors more money in two ways. We knew customers would love having KDP Select titles in the Kindle Owners’ Lending Library. But we’ve been surprised by how much paid sales of those same titles increased, even relative to the rest of KDP.”

On average, authors and publishers who participated in the Lending Library received an incremental 26% revenue in December, on top of the above-mentioned growth in paid sales, Amazon said.

This average number masks discrepancies, as the growth was much more substantial for popular authors; the top ten KDP Select authors, for instance, earned $70,000 in December from their participation in the Library. When taking paid sales into account, these authors actually saw their royalties increase by a whopping 449% month-over-month, Amazon notes.

In other words, Amazon is becoming a go-to player for authors, oftentimes without intermediaries. This is true for self-published authors, but also for celebrity writers. As we recently reported, Amazon Publishing has poached names like James Franco, Deepak Chopra and Tim Ferriss.